Oxygen lances are regularly used for a number of different purposes, from cutting metal objects such as beams and other structural members through to opening tapping holes in furnaces and crucibles.
The basic oxygen lance is a simple device that includes a metallic tube of around 4 m in length, and an oxygen supply. A supply of oxygen gas is continuously fed through the tube. Once the oxygen lance is ignited, the supply of oxygen sustains the continuous burning of the metal tubing. The result is a lance with an extremely high heat that is capable of melting and burning through a wide range of suitable objects. The metal tubing is consumed when the lance is in use, and therefore the lance needs to be fitted with fresh tubes at regular intervals to replenish the tubes as they are consumed by the use of the lance. A thermic lance operates in a similar way but includes wires (usually steel) inserted within the metallic tube to provide additional fuel for more heat generation.
One particular application of a lance is the use on furnaces to open tapping holes. Furnaces used in metallurgy run at very high temperatures. The refractory materials used to line the interior of these furnaces are capable of operating at these elevated temperatures, however specialized cooling panels are sometimes integrated into the furnace wall to extend the life of the refractory by conducting some heat away. Typically, a large furnace is fitted with a plurality of tapping holes that are used to tap molten metal contained in the furnace. When not in use, these tapping holes are blocked with a refractory mud or clay. This plug is inserted using a clay or mud gun or manually with a bot (clay plug wrapped in refractory fabric pushed in with a steel rod). The plug sets very hard and has a high resistance to heat. The combination of the plug of refractory clay and the cooling panels built into the furnace wall allow a plug of solidified metal to form adjacent to the refractory clay plug. This then remains in place until the next tapping operation falls due, upon which both the refractory mud plug and plug of solidified metal then needs to be removed.
One common way of removing the plugs is by burning through them using an oxygen lance. The tip of the lance burns at around 4,000° C., and is capable of burning through the refractory clay or mud plug material and the solidified metal in the tap hole. Another common way is to first break away the solidified refractory mud plug, thereby exposing the plug of solidifies metal that then needs to be re-melted in order to open the tapping hole.
It is common for a lance to need to be fitted with 10 to 20 fresh tubes in order to open just one tapping hole. This means that the operation needs to be halted 10 to 20 times while the lance is withdrawn from the hole and a fresh tube attached. Each time the lancing operation is halted, the tap hole re-cools to some degree. The environment where this operation needs to take place is inherently dangerous given the extreme heat of the furnace being operated on, the extreme heat of the oxygen lance itself, and the presence of oxygen around molten metals. The need to regularly stop the operation, withdraw the lance, fit it with a fresh tube and then re-insert the lance into the tapping hole adds considerable time to the tapping operation, as well as increases the exposure of the lance operators to risk.
It is an object of the present invention to overcome, or at least ameliorate, the aforementioned problems.